Abstract
CYCLOIDEA (CYC)-like genes, belonging to the plant-specific TCP transcription factor family that is named after TEOSINTE BRANCHED1 (TB1) from maize (Zea mays), CYC from Antirrhinum majus, and the PROLIFERATING CELL FACTORS (PCF) from rice (Oryza sativa), have conserved dorsal identity function in patterning floral zygomorphy mainly through specific expression in dorsal petals of a flower. Their expression changes are usually related to morphological diversity of zygomorphic flowers. However, it is still a challenge to elucidate the molecular mechanism underlying their expression differentiation. It is also unknown whether CINCINNATA (CIN)-like TCP genes, locally controlling cell growth and proliferation, are involved in the evolution of floral zygomorphy. To address these questions, we selected two closely related species, i.e. Petrocosmea glabristoma and Petrocosmea sinensis, with distinct petal morphology to conduct expression, hybridization, mutant, and allele-specific expression analyses. The results show that the size change of the dorsal petals between the two species is mainly mediated by the expression differentiation of CYC1C and CYC1D, while the shape variation of all petals is related to the expression change of CIN1. In reciprocal F1 hybrids, the expression of CYC1C, CYC1D, and CIN1 conforms to an additive inheritance mode, consistent with the petal phenotypes of hybrids. Through allele-specific expression analyses, we find that the expression differentiation of these TCP genes is underlain by distinctly different types of regulatory changes. We suggest that highly redundant paralogs with identical expression patterns and interspecific expression differentiation may be controlled by remarkably different regulatory pathways because natural selection may favor different regulatory modifications rather than coding sequence changes of key developmental genes in generating morphological diversity.
Highlights
BRANCHED1 (TB1) from maize (Zea mays), CYC from Antirrhinum majus, and the PROLIFERATING CELL FACTORS (PCF) from rice (Oryza sativa), have conserved dorsal identity function in patterning floral zygomorphy mainly through specific expression in dorsal petals of a flower
The results showed that the expression differentiation of CYC1C, CYC1D, and CIN1 coordinately promoted the morphological divergence of the dorsal petals that is characteristic of different types of zygomorphic flowers in the two species
We further found that cis-regulatory changes, trans-regulatory changes, and a complex of both changes contributed to the expression differentiation of CYC1C, CYC1D, and CIN1, respectively
Summary
BRANCHED1 (TB1) from maize (Zea mays), CYC from Antirrhinum majus, and the PROLIFERATING CELL FACTORS (PCF) from rice (Oryza sativa), have conserved dorsal identity function in patterning floral zygomorphy mainly through specific expression in dorsal petals of a flower. Regulatory Changes and Expression Differentiation changes of CYC-like genes usually bring about transformations of floral symmetry and modifications of floral morphology, mainly reflected in size and shape changes of the dorsal petals in the second floral whorl (Cubas et al, 1999b; Hileman et al, 2003; Busch and Zachgo, 2007; Gao et al, 2008; Song et al, 2009; Pang et al, 2010; Zhang et al, 2010; Howarth et al, 2011; Busch et al, 2012; Yang et al, 2012; Zhong and Kellogg, 2015). In spite of advances regarding cis- and trans-actions, the detailed relationship between regulatory variations of key developmental genes and phenotypic divergences, especially some important morphological novelties, has not been extensively explored yet, in plants (Rosas et al, 2010)
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